The invention relates to biological materials, methods of preparing such biological materials and uses thereof for example in ophthalmology. The invention may be used to produce anti-glaucoma drainage tubes for the surgical treatment of glaucoma, to produce collagen solutions to treat mild myopia and to produce pharmaceuticals for external use.
Biological materials have been extracted from raw material of animal origin, such as pig eye sclera, by treatment with alkali and acetic acid solutions as shown in Soviet Inventor""s Certificate No. 1747075, Cl. A 61 K 37/12. The material synthesized by this prior art method can be used in ophthalmological applications only after very lengthy and complex treatment. The material is characterized by extremely high solubility and low enzyme resistance. Hence, the material is not suitable for use in ophthalmology.
The present invention relates to biological materials and to the preparation of a biological materials for use in ophthalmology. In the invention, animal pericardium is provided and subjected to multiple steps of freezing and thawing in a salt solution. The pericardium is then incubated in a solution of ammonia and ethyl alcohol.
The present invention provides a method for the preparation of a biological material suitable for use in, for example ophthalmology.
It is an object of the invention to provide a method for the preparation of a material that is characterized by low solubility and high enzyme resistance.
Still another object of the invention is to provide a method to prepare a biological material from animal pericardium.
Pericardium is the connective tissue of the heart. The pericardium contains very few vessels or cells and its stroma consists primarily of collagen, which is relatively insoluble, and is relatively non-immunogenic. Moreover, a solution of collagen made from the pericardium is highly enzyme resistant. Enzyme resistance is extremely important for making collagen polymer products for use invivo. The high enzyme resistance of the present material prevents the formation of scar tissue invivo, for example when the present material, in the form of a glaucoma drainage tube, no scar tissue forms at the site of insertion of the tube into the eye. The method of the present invention provides a versatile biological material, which can be used extensively to produce a number of products such as scleroplastic materials, anti-glaucoma drainage tubes, materials for treating macular dystrophies and materials for synthesizing liquid medications.
In the method of the present invention, animal pericardium is first mechanically cleaned. The cleaning removes fat, vessels and other contaminants. The cleaned pericardium is cut into pieces of desired size and configuration and the pieces are rinsed in tap water. The animal pericardium pieces are then subjected to multiple steps of freezing and thawing in a salt solution. The salt solution is preferably a mixture of about 0.9% sodium chloride solution and distilled water in about 1:1 proportions of sodium chloride solution to distilled water. The multiple steps of freezing and thawing extract high molecular weight proteins and glycoproteins. The high molecular weight proteins and glycoproteins are the primary immunogenic components in pericardium tissue. It has been found that about 3 to 7 repeated steps, preferably about 4 to 6 and most preferably about 5 repeated steps of freezing and thawing are sufficient to remove all proteins and glycoproteins.
After the multiple steps of freezing and thawing, the animal pericardium pieces are incubated in a mixture of 1% ammonia solution and 1% ethyl alcohol solution in about 1:1 proportions of ammonia solution to ethyl alcohol solution. The solution is prepared and is poured over the pieces. The pieces in solution are incubated for a period of from about 36 to 68 hours, preferably from about 48 to 72 hours, the solution is then drained and replaced with fresh solution and the tissue is again incubated for from about 36 to 68 hours, preferably from about 48 to 72 hours. The incubation steps remove lipoprotein and lipids from the pericardium tissue. The pericardium should be incubated for at least 48 hours to remove the lipids. Incubation for more than 72 hours can break down the pericardium collagen.
After incubation, the animal pericardium is subjected to multiple rinsing steps. The rinsing steps comprise rinsing the pericardium for about 3 to 7 times, preferably for about 5 times, for a time period of from about 10 to 35 minutes, preferably for from about 15 to 30 minutes, each time in distilled water. During the rinsing, the pH of the waste rinse water is periodically determined and a Vidal ammonia test is conducted to determine when rinsing (complete removal of ammonial and alcohol) is complete. It has been found that the ammonia/alcohol solution is removed after rinsing five times for a time period of at least 15 minutes for each rinse. Shorter rinse times leave traces of ammonia and leave acidic pH levels. All ammonia is removed by using a rinse time period of 30 minutes.
After rinsing, the pericardium is sterilized in a solution of about 70% ethyl alcohol and is then irradiated with about 2.5 megarads of gamma irradiation. Specifically, the rinsed pieces are packed in vials containing the alcohol and are sterilized by irradiating the vials.
The following examples are intended to illustrate the invention without limiting its scope.